The Jungle is actually pretty low on symbolism, perhaps because it is a piece of journalism and social criticism. When a writer is trying to jab at real-life big business, he usually doesn't want to use too many difficult symbols or metaphors to do it. He doesn't want people to miss his message amidst a bunch of fancy, elusive imagery, so he'll keep his language straightforward. Or at least, that's the approach that Upton Sinclair seems to take.
Among the few things in The Jungle we might really call a symbol – in other words, an object that stands for something else – is the family house. This house represents the hopes and dreams that Jurgis and his family start out with. When they first buy the house, it's new and shiny-looking. Jurgis and Ona dream of setting aside a room to start out their married life together. They plan to furnish it and raise children together.
Soon, though, the reality of their situation starts to set in: the house is drafty and poorly built. It is sitting directly on top a drainage ditch for sewage, because there is no central sewer access this far outside of Packingtown. And the house isn't new at all; in fact, it is fifteen years old and has belonged to several unlucky generations of immigrant families. In other words, the house (and their hopes) may look great on the outside, but the realities are a lot grimmer than they had believed.
As Jurgis and Ona grow dissatisfied with their house, they also grow disenchanted with both married life and life in the United States. Jurgis gets injured on the job and becomes angry and resentful of being tied down to his family life. Ona attempts to hide the fact that she has been raped from Jurgis because she is afraid of making him angry. Jonas runs away, Antanas dies, Marija loses her job temporarily, all of the children go off to work, and they must keep struggling month after month to make the rent payments. At this point, the house is a symbol of the falseness of the American Dream. To newcomers, it looks shiny and desirable. But after you've lived here for a while, you realize that the dream is less easy to obtain than all the hype makes it sound. The whole "Land of Opportunity" thing isn't really all it is cracked up to be.
The final straw comes when Jurgis is thrown in prison. When Jurgis is in jail, he realizes that he is never going to make it in the American business world. He has too many disadvantages (for example, poverty, foreign birth, and lack of education) stacked against him. Once Jurgis gets out of jail, he finds that Ona is dying. So, not only are his dreams of financial success falling apart around him, but his hopes for marriage and children are also shattering. Given these disasters, it makes sense that the symbol for these dreams, the family home, is also taken away. Once Jurgis's family is evicted from their house, that is the final proof that they have totally failed to make it in their new country – Jurgis needs a new plan.
Obviously, the slaughterhouses in The Jungle are the subjects of Upton Sinclair's journalistic investigation, so they have a literal importance as the whole novel's reason for being. At the same time, Jurgis and his family's introduction to the modernized, mechanized slaughterhouse has an unfortunate symbolic resonance. Filled with pity, Jurgis watches a row of hogs going peacefully down a chute to the killing floor. He does not realize that he and his family, like those doomed pigs, are trooping equally quietly to their own doom. Consider the following description from Chapter 3, when Jurgis and his family first tour Brown's pork processing plant:
It was all so very businesslike that one watched it fascinated. It was pork-making by machinery, pork-making by applied mathematics. And yet somehow the most matter-of-fact person could not help thinking of the hogs; they were so innocent, they came so very trustingly; and they were so very human in their protests – and so perfectly within their rights! They had done nothing to deserve it, and it was adding insult to injury, as the thing was done here. (3.32)
The pigs are "so innocent" and come "so very trustingly" to the slaughter. We can compare their pitiable response to Jurgis's own eager volunteering to join the ranks of the meatpackers. He has absolute faith in the efficiency and value of these factories. He has no idea how much harm they will do to him. What is more, once Jurgis does realize how unjust the factory system is, he, like the hogs, is "perfectly within [his] rights" to protest. He has "done nothing to deserve" his fate. The slaughterhouses of The Jungle are not just convenient targets for Sinclair to expose to the public. They also serve as a larger metaphor for how American business treats its laborers, by luring them in to unsafe working conditions and then consuming their dedication and strength.